The Shadow of the Hole

By Bob Novella, on January 26th, 2012

Scientists may soon have a direct image of the black hole in the center of our galaxy.Using a virtual telescope as big as the earth, they may have for the first time apicture of the actual shadow a black hole.

Scientists met recently to discuss this project. It has probably one of the coolestnames for a telescope project: The Event Horizon Telescope.

Obviously building a real telescope as big as the earth would be just a tad expensive and time-consuming. It’s called a virtual telescope because it uses a common process called interferometry to combine the individual images of many telescopes into one image. The cool thing is that if you have enough telescopes, the resulting image is comparable to the image of one ginormous telescope that’s as big as the distance that separates all of them.

In the case of the Event Horizon project, there are 50 radio telescopes around the world that, when combined, will give us an image as if we had one radio telescope as big as the earth. It will be far and away the most detailed picture of the center of our galaxy and our very own supermassive black hole that’s ever been taken.

This is no small feat considering that the 4 million solar-mass black hole that’s in the center of our galaxy is 26,000 light years away and only as big as Mercury’s orbit. That’s 153 quintillion miles away. Imaging it is like seeing a grapefruit on the moon. You may think: “but black holes devour everything, even light, they’re by definition invisible.”

True, but we can see the immediate vicinity around it.

Dimitrios Psaltis Associate Professor of Astronomy and Physics at the University of Arizona recently said:

“We expect to see the swirling of matter going into the black hole in real time, What we’re really hoping to see is how the black hole is fed.”

It’s even better than that though. The glowing matter around a black hole should clearly delineate it’s shadow. This shadow is actually the silhouette of its event horizon which is the boundary in space-time around the hole such that once you cross it, there’s no coming back even if you’re traveling at the speed of light.

So what may we see with such a view? Lotsa cool stuff:

real-time flaring events occurring near the black hole

rotation of the supermassive black hole

accretion disk dynamics.

extreme relativistic effects predicted to be acting on the volume of space surrounding it

This leads us to Einstein and a test of General Relativity. This theory predicts that this shadow should be perfectly circular. If it’s not, then he’s got some splainin to do and we may find that General Relativity needs some modification. Really though, is there any doubt that this billionth test of his theory will succeed? It would be kinda cool if we found some special case and some new physics but I’m not holding my breath.

Still though, I’ve never been this excited by the prospect of seeing a shadow.